hi Rich,
I'd say that the distance travelled is the integral over the
instantaneous speed,
or the average speed times elapsed time ; for constant decelleration,
the average speed is half the initial speed, so the time nescessary is
t = s/(v/2) and a= - v/ t = - v^2 /( 2 s ) or abouts.
For your example that would be a= - 4^2 /( 2 * 25) = - 0.32 m/s^2
You learn to do stuff like that in your head after a while.
wouter.
Richard Cooper wrote in message <72tqhj$iml at smc.vnet.net>...
>Hi All,
>
>I am using Mechanical Systems and need help modelling motion where the
>velocity of a body is dependent on its distance from a set point.
>
>For example, I have a body moving in 1D which starts with a speed of 4
>m/s and is subject to a constant but unknown deceleration. The point at
>which the body comes to rest must be 25 m from the starting point.
>
>What is the best way to model this system (and calculate the
>decleration)?
>
>The following might be a good starting point. It needs one more
>constraint.
>
>fixed = 1;
>flyer = 2;
>start = {0, 0};
>pointOfRest = {0, 25};
>
>SetConstraints[
> RotationLock1[1, flyer, fixed, 0],
> RelativeY1[2, Point[flyer, 0], 0],
> DirectedDistance1[3, Point[flyer, 0], start, {1, 0}, 4T-(a T^2)/2],
> Constraint[5, {}, {a, 1}]
>]
>
>Cheers,
>
>Rich.
>